1. Field of the Invention
The field of the present invention is designing dies for stamping sheet metal parts. More particularly the present invention relates to designing dies for stamping sheet metal parts which compensate for the tendency of sheet metal parts to spring back after a stamping operation, so that the part process from the die will more exactly match a design intent profile of a part.
2. Background of the Invention
Most automotive vehicles have a plurality of metal stampings which are utilized both in the chassis and automotive vehicle body. In many instances the stamping workpiece starts out as a thin sheet of metal. The metal is pressed between two dies which form the workpiece in the desired configuration. After the stamping operation, the workpiece is trimmed and delivered to another workstation for further metal working operations or assembly with the vehicle. The stamping operation forms the workpiece by plastic deformation. However, some of the deformation which occurs to the workpiece will still be elastic in nature. Therefore, after removal from the dies, certain portions of the workpiece will tend to elastically deform to relieve the residual stress. This relieving of residual stress is often referred to as spring back. Trial and error has taught tool designers that for a predetermined workpiece profile, the die utilized to stamp the workpiece must be modified so that the workpiece will spring back after pressing to form a workpiece within predetermined dimensional limitations.
Prior to the present invention, most of this compensation in die design to accommodate spring back was a function of the knowledge and experience of the tool and die designer. Often the above-noted process of trial and error caused a major expense due to design and redesign of dies. The prior trial and error method also required significant expenditures of time.
Attempts have been made to mathematically quantify the design process of stamping dies to be less dependent upon the knowledge and experience of a tool and die maker. Many of the prior mathematical computational methods of designing dies which could accommodate for spring back require the utilization of computers with a larger amount of power and also require extensive amounts of time to bring forth satisfactory results. Another problem with many prior predictive techniques is that they fail to converge in some circumstances, such as in case of complex tooling geometries or in case of different materials. For example, if a first iteration of the predicted die surface was corrected too far so that the die would form a part that was over bent, the predicted technique could not converge back to provide a die which would form a workpiece in a non over bent condition.
Another problem with prior predictive techniques was lack of a good method to start out with an initial corrected die which differed in profile from the design intent profile of the workpiece. Experience has taught those in tool die arts that certain modifications will be needed. Therefore, it is desirable to start out with a mathematical technique which can predict results starting out with a die which has already been modified from a profile of a design intent workpiece.
Still another problem with prior predictive techniques was that there was no way to take advantage of empirical data which was generated from actual tryout dies.
It is desirable to provide a method of designing a stamping die which can accommodate needed changes due to the spring back characteristic of the stamped metal workpiece in shorter time intervals with more predictable results. It is further desirable to provide a method of designing a stamping die wherein the predicted result converges to a more accurate solution. It is still further desirable to provide a method of designing a stamping die which can take advantage of empirical data gathered from tryout dies.